[MACKENZIE] HISTORICAL AND STRUCTURAL GEOLOGY 127 



The Palaeozoic is taken as 15,000 feet thick, a figure which at any 

 rate represents the order of magnitude of the sediments of that era. 

 Near the main line of the Canadian Pacific railway the thickness of the 

 Palaeozoic is given as 30,000 feet by McConnell (21,b). The thickness 

 given by Allan in the Ice River area is 28,000 feet for the Cambrian, 

 Ordovician, and part of the Silurian only (3, a) . These thicknesses are 

 north of the region considered. In Flathead valley near the boundary 

 there are 5,000 feet of Devono-Carboni ferons rocks exposed (26,b), 

 and in the North Kootenay pass there are several hundred feet of 

 Middle Cambrian strata (1). In view of these figures, 15,000 feet is 

 considered a moderate figure for the thickness of the Palaeozoic 

 measures. No attempt has been made to indicate variations of thick- 

 ness in the rocks of this era, though they undoubtedly exist. 



The Mesozoic strata are shown as decreasing in thickness from 

 west to east, which is in accordance with what is known of the Koot- 

 enay and Fernie formations. As the Mesozoic formations were 

 derived from a westward land mass there is little doubt that the 

 rocks of that era are thicker toward the west. Accordingly they are 

 shown here with a thickness of 15,000 feet thinning to 10,000 feet in 

 the east. McEvoy found 12,000 to 13,000 feet of Cretaceous strata 

 alone in the Crowsnest basin (22a), and Stewart gives a maximum 

 thickness of 12,000 feet above the Fernie in the foothills of south- 

 west Alberta (41,f). The figures used here are. therefore, sufticiently 

 representative for the purposes of this paper. 



A significant difference in the method of action of the compressive 

 stresses is apparent from the present day distribution of the Cretaceous 

 rocks. Near the International Boundary Precambrian rocks are at 

 the surface in the western area, while near the North Kootenay pass 

 Mesozoic rocks outcrop all the way across except in the overthrust 

 zone of older strata. Apparently, therefore, compression was accom- 

 panied by uplift in the west at the boundary, causing denudation of 

 the higher rocks, while farther north a corresponding uplift did not 

 take place, leaving the Mesozoic rocks still exposed at the surface. 

 It is possible that transverse faulting across the north end of the 

 MacDonald range may in part account for this Mesozoic area to the 

 north. 



Taking first the section at the boundary, Section B, Figure 2, 

 illustrates an early stage in the compression of the region. In this, 

 as in subsequent sections, the shortening shown is qualitative, as no 

 attempt has been made to estimate the actual shortening (which may 

 have been considerable) of the region involved in the folding and over- 

 thrusting. These early stresses are supposed to have compressed 



